Predatory coral bring down jellyfish by working together

For the first time, scientists have demonstrated that corals can work cooperatively to capture jellyfish.

The team observed the bright orange Astroides calycularis, which lives on sea walls and caves in the Mediterranean Sea, snagging mauve stinger jellyfish that became trapped by ocean currents.

Coral polyps first grab onto a jellyfish’s bell, and then others will begin ingesting the jellyfish’s arms in a process that takes just a few minutes.

While it might lack the coordinated attacks that lions or wolves can mount against their prey, a species of coral has shown that it, too, can pull together a collaborative hunting effort.

A team of scientists recently reported in the journal Ecology that coral species called Astroides calycularis can capture mauve stinger jellyfish (Pelagia noctiluca).

“Although both species have been known for years, we had no idea that the coral could catch and eat these jellyfish,” Fabio Badalamenti, a marine ecologist with the Italian National Research Council in Rome and a co-author of the study, said in a statement.

It’s the first time that scientists have documented this type of “collective” behavior, Badalamenti and his colleagues write.

A. calycularis, sometimes called orange coral for its brilliant color, lives only in the western Mediterranean Sea, where it latches onto vertical walls and the sides of underground caves in tightly packed groups. Most often, the polyp extending out from the rocky surface to which the coral has fastened itself measures 4 or 5 millimeters (0.16 or 0.2 inches), the authors write, though it can grow to twice that length.

Between 2010 and 2017 in different places throughout the Mediterranean, the team noticed that currents sometimes trap a common type of jellyfish called the mauve stinger against walls or in the overhanging roof of an undersea cave covered with A. calycularis coral.

Moving in for a closer look, the researchers found that, initially, a few corals lock onto the bulbous bell of the jellyfish. Then, other individual corals grab onto and begin eating the jellyfish’s arms. The whole attack takes one to five minutes, the authors say.

It’s not always entirely successful for the coral. Jellyfish seem to have the ability to get away sometimes, though the dead jellies that the team found at the bottom of the sea, their bells perforated, indicate that their efforts to flee the hungry coral and survive can be futile.

The researchers figure that corals don’t prey on enough jellyfish to make much of a dent in the population. But, they write, catching such prey is “arguably an important resource” for orange coral, an animal that mostly siphons tiny zooplankton from the water.

Their findings are also an important reminder that there’s still more to learn about the interplay between even well-known species.